The squish band looks very close to the valve seat.
is that not a risk of getting a hot spot ?
Looks the same as my stock R90S heads (just had them off for new rings). The gap between the valve seats is probably smaller. So I wouldn't think there's a risk.
s a bit of a task to drill it out.

Your work is fantastic Im enjoying this thread and its giving me some inspiration, love it cant wait to see you complete it .